For switch mode power supply (SMPS) converters the size and efficiency are important due to the ever shrinking size of devices. A small converter with a high output power needs a high efficiency to keep the component temperature and casing temperature low. Improvement in efficiency can be achieved by applying synchronous rectification (SR) in the AC to DC output stage of the SMPS converter. The ideal efficiency improvement that can be achieved by adding a SR with respect to rectification by diodes is the diode voltage divided by the output voltage.
The SMPS with SR converter typically includes two switches, a primary switch and a secondary switch. The switches should not conduct at the same time and for operation in “continuous conduction mode” the “make-before-break” technique of switching the two switches is employed to prevent large reverse current and large voltage peak that degrades the efficiency. The “make-before-break” technique is a configuration in which the new connection path is established after the previous contacts are opened. In other words, the “off” times of the two switches overlap for a time being during each switching cycle. The overlap period may be referred to as “dead time.”